1. Field of the Invention
The present invention relates to a sheet processing apparatus, an associated method, and an image forming apparatus.
2. Description of the Background Art
As a technique concerning sheet processing apparatuses, for example, Japanese Patent Application Laid-Open Nos 2001-19252 and 2001-199616 disclose a technology relating to a sheet processing apparatus that applies predetermined processing to a sheet-like recording medium (sheet). As shown in FIG. 1, the sheet processing apparatus staples the sheet bundle fed from a pair of discharging rollers 505 on to a staple tray 501. The sheet processing apparatus includes a sheet guide member 507, which is freely rotatable so as to guide the sheet fed from the discharging rollers 505 to the staple tray 501.
As shown in FIG. 1A, in an initial state, the sheet guide member 507 is located in a position that obstructs a nip portion of the discharging rollers 505. When a sheet proceeds into the discharging rollers 505 in that state, the sheet guide member 507 rotates in the direction shown by the arrow R due to being pushed up by the leading edge of the sheet and opens the nip portion of the discharging rollers 505.
After discharging the sheet from the discharging rollers 505, as shown in FIG. 1B, the sheet guide member 507 rotates in a direction shown by the arrow S toward the initial state due to its own weight. Then the sheet guide member 507 guides the sheet to the staple tray 501 by pressing the trailing edge of the sheet. As shown in FIG. 1C, the sheet guide member 507 prevents the sheet from conveying backward (the direction shown by the arrow T) by obstructing the nip portion of the discharging rollers 505 in this state. Afterward, as shown in FIG. 1D, the sheet fed from the discharging rollers 505 is stacked on the staple tray 501.
However, such a sheet processing apparatus can generate a paper feed malfunction, as illustrated in FIG. 2. For example, if a soft sheet or a sheet that is curled to the staple tray 501 is discharged from the discharging rollers 505, the sheet hangs loose as shown FIG. 2B after the leading edge of the sheet has passed the nip portion of the discharging rollers 505.
As shown in FIG. 2C, the leading edge of the sheet discharges to the staple tray 501 while being pressed in the direction shown by the arrow U by the sheet guide member 507, which is rotated to its initial state by its own weight. In this state, when the leading edge of the sheet touches the staple tray 501, the edge is curled as shown FIG. 2D and it causes a conveying malfunction.